Timing chain check.


3 replies to this topic
  • yzhaulin

Posted July 13, 2009 - 09:29 AM

#1

After seing a lot of timing chain questions and having the piston hit the valves on my own bike. I decided to try and come up with a way to check the timing chain for stretch.
What I came up with is this.
While having the cam cover off during valve clearance checks or other reasons.
1. Remove the bolt from the end of the tensioner.
Posted Image

2. Put tension on the chain between the gears like below.
Posted Image

3. While keeping tension on the chain as above, use a small screwdriver and turn(releasing) the tensioner screw (clockwise) and count the turns it takes to fully release the tensioner. Do not release tension on the cam chain with your finger as doing so will allow the chain slack to fall to the crank gear and allow the chain to possibly skip a link and be out of time. holding pressure on the chain as above will keep the chain tight to the sprockets and not skip.
Posted Image
Your chain/sprockets should look like this when the tensioner is fully retracted.
Posted Image
5. Count the number of turns it takes to fully retract the tensioner. My 01 426 was just over 4 full turns to fully retract. if you count anything close to 4 turns your chain is stretched and should be replaced. After replacing the chain and rechecking with this procedure it was at approx 2 turns.
6. Be sure to release the tensioner by roatating the screw counterclockwise a small amount about 1/4 turn before releasing tension on the chain with your finger,remove your finger slowly to allow the tensioner to re engage the guide.
7. With a new chain installed or checking your old one,(with the tensioner in its normal position) lay a feeler guage across the head surface between the cams and apply pressure, you should have to put a decent amout of pressure on the chain to make it contact the chain like this.
Posted Image
This is a procedure I came up with to hopefully help avoid cam chain failure and top end damage, Hope this helps others. It works for me so far.

  • grayracer513

Posted July 13, 2009 - 09:53 AM

#2

There are two things wrong with this. As a concept, the idea is sound, but slightly flawed as presented.

1) The engine must be at or near TDC in the timing position (on the compression stroke, with the cam lobes out and up). If this is not done, the spring pressure on the cam lobes can potentially "drive" one of the cams and cause it to slip.

2) There is no danger whatsoever of the chain dropping free of the crank sprocket at TDC/compression while the chain remains over the cams, with or without the tensioner active.

3) This is the main problem: production variances will cause the tensioner to run against a new chain a different number of turns on any two engines and/or with any two tensioners. The threads within the tensioner are very fine, and a very small difference in any associated dimension within the entire system can cause the retraction distance to change by a full turn.

However, if you check this out with a new bike, or one with a new chain in place, it can be used as an indicator of chain wear as long as that chain and tensioner remain paired, so it isn't a bad idea.

The more common problem with the newer bikes seems to be that the chain sometimes develops tight, or kinked links as it wears. This causes the chain to remain artificially short on the slack side of the run, and fools the tensioner into not taking up the actual slack. At some point then, the chain slips on one of the cam sprockets.

To avoid this, periodically release the tension on the chain, press down on the top run as shown here, and check the chain for free motion. Re-tension it, turn it over to the next TDC/compression, and check again, repeating a few times.

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  • 642MX

Posted July 13, 2009 - 07:37 PM

#3

Let me throw this out there.... As important as a timing chain is, and knowing they are the weakest link in the YZF, they should just be replaced. Spending time trying to check them is useless in my opinion.

  • grayracer513

Posted July 13, 2009 - 08:02 PM

#4

Frequent replacement is a good idea of course, annually in most cases, but it doesn't hurt to check them even more often than that, or to know how.





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